The premise of bonds is simple: you invest your money to an entity and, after a set period of time, that money matures and can be collected for more than what you invested. Some of the more popular bonds are government bonds, which have been used in the past to fund wars, public utilities, and various federal and state projects.
The main caveat to bonds is their limited returns and the possibility of that yield barely even surpassing inflation. However, the security of bonds is priceless. Bonds are all but sure things and even if the issuer goes bankrupt, bond holders (lenders) are the first to be paid out. Bonds have their place in any portfolio, as they provide lockdown stability and even some growth.